IEEE 802.11 is a set of standards for implementing wireless local area network (WLAN) communication in the 2.4, 3.6, 5, and 60 GHz frequency bands. Within the IEEE 802.11 standards, IEEE 802.11ac covers very high throughput with potential improvements over IEEE 802.11n, IEEE 802.11ah covers Sub 1 GHz sensor network and smart metering, and upcoming IEEE 802.11ax considers the improvement of spectrum efficiency to enhance the system throughput in high-density scenarios of wireless devices and will become a successor to IEEE 802.11ac.
When WLAN is deployed in the outdoor scenarios, stations (STAs) can experience time-varying channel conditions. Time varying channels are mainly caused by Doppler effect, due to movement of STAs or the fast-moving objects around STAs. In a first scenario, speed up to 3 kilometers per hour (kmph) for all clusters for UMi and Uma model. In a second scenario, the second and third clusters of UMi and UMa models assigned a speed of 60 kmph and the rest of the clusters assigned 3 kmph.
Channel variation is an important feature of channel condition and should be feedback for enhancing the system performance of WLAN. In wireless communications systems, travelling pilots or mid-amble can be used to combat time-varying channels by enabling channel tracking. For backward compatibility and simplicity, however, traveling pilots or mid-amble may not be applied for every packet. Furthermore, there is no existing mechanism for feedback the channel variation information. As a result, the transmitter has no knowledge about the time-varying channel condition of each receiver.
Signaling and feedback schemes of channel variation information from WLAN receiver can help WLAN transmitter to decide when to apply travelling pilots or mid-amble in the transmission. The information of channel variation needs to be obtained by the receiver, and then fed back to the transmitter to assist various decision making for the next transmission and thereby enhancing the system performance of WLAN.